The present invention relates generally to an imaging module and an imaging reader for, and a method of, detecting objects associated with targets to be read by image capture.
Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read targets, such as one- and two-dimensional bar code symbol targets, and/or non-symbol targets, such as documents, over a range of working distances relative to each reader. An imaging reader includes a housing for supporting an imaging module, also known as a scan engine. In a hands-free mode, such as at a fixed position kiosk or at a stationary, point-of-sale (POS) workstation, the imaging module is mounted in a housing having at least one window to which objects associated with, e.g., bearing, the targets to be read are either presented, or across which the targets are swiped. The imaging module includes an imaging assembly having a solid-state imager or imaging sensor with an array of photocells or light sensors, which correspond to image elements or pixels in an imaging field of view of the imager, and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged over a range of working distances relative to the module, and for projecting the return light onto the array to initiate capture of an image of the target. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electrical signals corresponding to a one- or two-dimensional array of pixel data over the imaging field of view. In order to increase the amount of the return light captured by the array, for example, in dimly lit environments or for far-out targets located relatively far from the window, the imaging module generally also includes an illuminating light assembly for illuminating the target with illumination light over an illumination field for reflection and scattering from the target.
Some imaging modules continuously capture and attempt to process targets without regard to whether or not an object is actually in the imaging field of view. However, this consumes and wastes electrical energy and degrades module component lifetimes. To alleviate these problems, the art has proposed periodically and automatically activating, i.e., waking-up, the imaging module, for example, with a very low duty cycle (about 10%). Thus, the imaging module wakes up for a very short period of time to scan the imaging field of view and tries to detect a presence of an object therein. However, this creates sluggishness in the reader's performance and delays in processing, which can be perceived as an engineering defect, and also wastes electrical energy.
The art has also proposed the use of additional hardware components such as dedicated object sensors, each having an object detection field, which is at least partly commensurate with the imaging field of view, for activating the imaging module only if an object bearing a target is detected within the detection field. Such dedicated sensors may include motion sensors for detecting the movement of objects in the field of view by, for example, comparing the positions or locations of edges of captured images in the field of view between consecutive image frames. However, motion sensors can be falsely triggered, for example, by people or customers walking past the motion sensors, or by an operator's hands or body inadvertently passing through the field of view, or by objects not bearing targets entering the field of view. Such false triggering wastes electrical energy.
Such dedicated sensors may also include proximity sensors, typically one or more pairs of infra-red (IR) light emitters and detectors, each pair being operative for detecting a change or interruption in the IR light passing in a light path between the respective pair. In such IR light-based sensors, the range in which an object can be detected is dependent on the amount of IR light detected by each IR detector and, in turn, is dependent on the size and location of the object. A small object might not trigger the proximity sensor, thereby degrading reading performance. Typically, IR light-based sensors require optical alignment procedures to be performed, which increases manufacturing time and cost.
The deployment of dedicated object sensors generally undesirably increases the size, cost, electrical power consumption, and complexity of the imaging module, and, in turn, of the overall reader. The object detection field of an object sensor may not, in some cases, exactly match the imaging field of view of the module, thereby creating dead zones and compromise reading performance.
Accordingly, there is a need to reduce the size, cost, electrical power consumption, and complexity of the imaging module and of the overall reader, to efficiently and reliably effect object detection for objects, even of small size, without deploying additional hardware components or effecting optical alignment procedures, and to generally improve overall reading performance.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.